<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      //       var a = 40;
      // //运行结果是10
      //       function fun1() {
      //         console.log(a);
      //         var a = 30;
      //         fun2();
      //         function fun2() {
      //           var a = 20;
      //           fun3();
      //           function fun3() {
      //             var a = 10;
      //             console.log(a);
      //           }
      //         }
      //       }

      //       fun1();
      {
        var c = 0;
        let a = 10;
        const b = 50;
        console.log(c);
        console.log(b);
        console.log(a);
      } //js代码可以用一个大括号将一段代码括起来，表示一个域
      console.log( c);
      console.log(b);
      console.log(a);
    </script>
  </body>
</html>
